Various types of polyurethane are produced by polymerization of diisocyanates, such as 4,4′-methylenebis(phenyl isocyanate), abbreviated to MDI, or toluene 2,4-diisocyanate, abbreviated to TDI, with polyether polyols or with polyester polyols. The polyether polyols used in these processes are obtained through alkoxylation of polyhydroxy-functional starters (precursors), e.g., glycols, glycerol, trimethylolpropane, pentaerythritol, sorbitol or sucrose. Production of polyurethane foams uses additional blowing agents, e.g., pentane, methylene chloride, acetone or carbon dioxide. An indispensible factor for reproducible industrial production of foam (moldings) is stabilization of the polyurethane foam by a surfactant. The materials typically used, other than a few purely organic surfactants, are silicone surfactants, since such surfactants have a high capability for stabilization at interfaces.
A great number of different types of polyurethane foams are known, examples include flexible foam, high resilience foam, ester foam, rigid polyurethane (PU) foam and rigid polyisocyanurate (PI) foam. The stabilizers used in these processes have been developed specifically for the respective final application and usually exhibit significant performance difference when used in the production of other types of foam.
Recently, modified silicone surfactants, in particular polysiloxane polyether copolymers, have been developed for a very wide variety of types of foam. These polysiloxane polyethers differ in relation to the structure of the polyether moieties present.
DE 102004001408 describes the use of polyether siloxanes having a block structure as stabilizers in polyurethane foams. DE 10 2006 042 338 describes the use of polyethers comprising urethane groups or comprising urea groups for stabilizing polyurethane foams. DE 102008043343 describes silicone-polyether block copolymers with defined polydispersity in the polyoxyalkylene moiety and their use as stabilizers for the production of polyurethane foams. DE 102010063241 and DE 102010063237 describe silicone stabilizers for rigid polyurethane foams or for rigid polyisocyanurate foams. DE 102011003150 describes silicone-polyether block copolymers having high-molecular-weight polyether moieties and their use as stabilizers for the production of polyurethane foams. DE 102011003148 describes the use of silicone-polyether block copolymers having high-molecular-weight non-end-capped polyether moieties as stabilizers for the production of low-density polyurethane foams.
EP 0 900 811 describe the addition of cyclic organic carbonates in the production of polyurethane foam, in particular in formulations for flexible polyurethane-polyether foam.
EP 0 798 327 describes a process for the production of polycarbonate-co-polyetherdiols in the form of a two-stage process. In a first step, a polyether glycol is reacted with bisdimethylcarbonate in the presence of a basic catalyst to give a polyetherdiol bisdimethylcarbonate so as to permit conversion, in a subsequent second step, after distillative removal of the excess of dimethyl carbonate and removal of the basic catalyst, into a polycarbonate-co-polyetherdiol through an acid-catalyzed transesterification. One disadvantage of such a process is the work-up of the intermediate and the need to change the catalyst system.
U.S. Pat. No. 5,525,640 provides silicone-based wetting agents and their use in polyurethane foam blown by inert gases. In particular, the '640 patent discloses that a polyurethane foam subject to inert gas pressure can ideally be stabilized by a polyethersiloxane having a comb-type structure, where the ethylene oxide content in the polyether makes up less than 37% of the total alkylene oxide content. The teaching is supported by comparative foaming experiments in a mechanically produced foam system and also in a liquid-CO2-blown foam system, using comb-type polyethersiloxanes entirely capped with acetoxy groups or with methyl groups. Alternative end groups disclosed, which cap the polyoxyalkylene branch, are —C(O)Z′, —C(O)OZ″ or —C(O)NHZ′, where Z′ comprises monofunctional alkyl or aryl groups of from 1 to 8 carbon atoms. No particular significance is attributed to these end groups, and this is also apparent from the fact that preference is given to the acetate end cap and the methyl end cap.
WO03/091320 discloses silicone-based wetting agents which are particularly suitable for providing flame retardancy to CO2-blown polyurethane foam with fine cell structure. The teaching of U.S. Pat. No. 5,525,640 is utilized, and comb-type polyethersiloxanes are disclosed, the ethylene oxide content in the polyether in the comb-like polyethersiloxanes making up less than 37% of the total alkylene oxide content, where —C(O)Z′, —CC(O)OZ′ or —C(O)NHZ′ are mentioned alongside the specifically disclosed end caps using acetate groups and methyl groups in the polyoxyalkylene moiety, where Z1 comprises monofunctional alkyl or aryl groups of from 1 to 8 carbon atoms.
Similarly, U.S. Patent Application Publication No. 2010/0286295, which relates to silicone-based wetting agents for use in polyurethane foams derived from vegetable-oil polyetherols, discloses-silicone polyethers comprising alkyl groups. This publication also describes the possibility indicated in WO03/091320 of the organocarbonate end cap. Preference is again to use an acetate or methyl end cap in the '295 publication.
One area on which very high value is currently placed is environmentally friendly process technology. Increasing use is made of carbon dioxide (CO2) as a blowing agent, in order to avoid the use of blowing agents such as methylene chloride or chlorofluorocarbons. There are many silicone stabilizers that are not suitable for the foaming process using CO2 as a blowing agent.